406 overtemperature issues

I own a 2004 model automatic transmission 406. No matter how hard the vehicle is on the flat road, the temperature is constant at 90. But when I go uphill at 100km+ speed, the temperature lasts up to 100 120 130. When I climb the same slope with a speed of 60 70 km, the temperature is constant, there is no water loss in any way. When the temperature exceeds 100, the water boils and drains naturally. I rode for weeks in heavy traffic on the straight road, the temperature does not exceed 90. It is constant. I go up to 200km on the flat road, still at a constant temperature. There has been a problem for the past few days. When the engine of the vehicle is cold, it gets a great power and rears up, but when the engine warms up and reaches 90 degrees, the revs increase, but the vehicle does not officially go away. When going uphill, the engine oil temperature lasts up to 130 140 only. What do you think could be the reason?